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COLUMBIA. GLACIER 267
there being an advance during the same period of ten years in the central part of the tidal cliff.1
In 1899 the point of the ice cliff projecting farthest south was near the center of the main cliff and it was in about the same position in August, 1909, though a little farther west. There were numerous •minor promontories and coves in the ice cliff. The cliff was almost entirely free from debris, except in the areas reached by the western lateral moraine and one medial moraine near the western border. It was snowy white near the top and more glassy near the base, where there were also occasional minor dirt bands, also suggesting the shallowness of the bay here. Photographs, taken in 1909, from two sites on the small island north of Heather Island that were occupied by members of the Harriman Expedition ten years before, showed a slight advance of the main ice front in Columbia Bay and an increase in the height of the cliff.
With the advance of the cliff on the western margin there was a great increase in the height of effective wave work there, resulting in the destruction of vegetation by the great waves generated by the discharge of icebergs from the front of the glacier. Along the inner face of the beach and at the base of the cliff, vegetation had grown with relation to the height of wave work appropriate to an ice cliff a quarter of a mile or more away. When the ice cliff advanced this distance the waves began to wash up much higher, and in August, 1909, beach cobbles and sand had been thrown back among the trees, from some of which the bark had been eroded several inches above the ground. Some trees were killed by the sand and salt water, and some were broken off. Lichens and moss were removed from the rocky cliffs fifteen to twenty-five feet above high tide, soil had been washed down, and at the head of one chasm on the coast a wave had recently splashed so high out that it had ripped up a strip of turf and flung it, bottomside up, into the forest at the head of the chasm.
The main ice cliff, which descends nearly 500 feet in the last quarter of a mile, though frequently discharging icebergs, more by cascading down the front than by rising from below the surface, was far less active than Hubbard Glacier in Yakutat Bay. The terminal cliff of Columbia Glacier is nearly 200 feet higher than that of Hubbard Glacier, but it is far less steep. Columbia Glacier has a broken front down which ice fragments cascade whereas Hubbard Glacier front is in places nearly, if not quite, vertical for 300 feet. There were no large icebergs, apparently because the ice front stands in shallow water, and there were only a moderate number of small bergs, perhaps because of the easy escape they have to the open waters of Prince William Sound.
Neither the main ice ^liff nor the eastern ice cliff projects as far as the Heather Island terminus, perhaps partly because the latter is opposite the center of the glacier, but also in part on account of the more rapid recession in salt water than on the land. Because of this difference, the ice front of Columbia Glacier is sinuous, with moderate re-entrants in the two places where in contact with the salt water, and with a notable projection where resting on the island.
In June, 1910, the main ice cliff was from 400 to 600 feet farther south than in August, 1909, the greatest advance (Fig. 80) having come in the portion a little west of the middle. The rate of actual advance of that portion of the glacier ending in water cannot be determined because iceberg discharge causes the shortening of the glacier while it is advancing. The rate must be considerably in excess of two feet a day, however,
> Grant. U. S. and Higgins. D. F., Bull. Amer. Geog. Soc., Vol. XLII, 1910, Fig. 6, p. 728.